A Peek Inside Quality Management Systems



In electronics, printed circuit boards, or PCBs, are used to mechanically support electronic components which have their connection leads soldered onto copper pads in surface mount applications or through rilled holes in the board and copper pads for soldering the component leads in thru-hole applications. A board design might have all thru-hole components on the top or element side, a mix of thru-hole and surface area install on the top side only, a mix of thru-hole and surface mount elements on the top and surface area mount elements on the bottom or circuit side, or surface area mount parts on the top and bottom sides of the board.

The boards are also utilized to electrically connect the required leads for each part utilizing conductive copper traces. The part pads and connection traces are engraved from copper sheets laminated onto a non-conductive substrate. Printed circuit boards are created as single sided with copper pads and traces on one side of the board only, double sided with copper pads and traces on the leading and bottom sides of the board, or multilayer styles with copper pads and traces on the top and bottom of board with a variable variety of internal copper layers with traces and connections.

Single or double sided boards consist of a core dielectric material, such as FR-4 epoxy fiberglass, with copper plating on one or both sides. This copper plating is engraved away to form the real copper pads and connection traces on the board surfaces as part of the board production process. A multilayer board consists of a number of layers of dielectric product that has been fertilized with adhesives, and these layers are used to separate the layers of copper plating. All these layers are aligned and after that bonded into a single board structure under heat and pressure. Multilayer boards with 48 or more layers can be produced with today's technologies.

In a normal 4 layer board style, the internal layers are frequently utilized to offer power and ground connections, such as a +5 V aircraft layer and a Ground airplane layer as the two internal layers, with all other circuit and part connections made on the leading and bottom layers of the board. Really complex board designs may have a a great deal of layers to make the numerous connections for various voltage levels, ground connections, or for linking the lots of leads on ball grid variety devices and other large integrated circuit bundle formats.

There are normally 2 types of material used to build a multilayer board. Pre-preg product is thin layers of fiberglass pre-impregnated with an adhesive, and is in sheet form, normally about.002 inches thick. Core product is similar to an extremely thin double sided board in that it has a dielectric product, such as epoxy fiberglass, with a copper layer transferred on each side, usually.030 thickness dielectric material with 1 ounce copper layer on each side. In a multilayer board design, there are two methods utilized to build up the preferred variety of layers. The core stack-up approach, which is an older innovation, uses a center layer of pre-preg product with a layer of core material above and another layer of core product below. This combination of one pre-preg layer and two core layers would make a 4 layer board.

The movie stack-up technique, a newer innovation, would have core material as the center layer followed by layers of pre-preg and copper material built up above and below to form the final variety of layers needed by the board style, sort of like Dagwood constructing a sandwich. This method enables the manufacturer flexibility in how the board layer densities are integrated to fulfill the finished item thickness requirements by varying the variety of sheets of pre-preg in each layer. As soon as the material layers are completed, the whole stack is subjected to heat and pressure that causes the adhesive in the pre-preg to bond the core and pre-preg layers together into a single entity.

The process of producing printed circuit boards follows the steps listed below for the majority of applications.

The process of determining materials, procedures, and requirements to satisfy the customer's specs for the board design based upon the Gerber file info supplied with the order.

The process of transferring the Gerber file data for a layer onto an etch resist movie that is placed on the conductive copper layer.

The traditional procedure of exposing the copper and other locations unprotected by the etch resist movie to a chemical that removes the unprotected copper, leaving the protected copper pads and traces in place; more recent processes use plasma/laser etching rather of chemicals to remove the copper material, enabling finer line meanings.

The process of aligning the conductive copper and insulating dielectric layers and pushing them under heat to activate the adhesive in the dielectric layers to form a strong board material.

The procedure of drilling all the holes for plated through applications; a 2nd drilling process is utilized for holes that are not to be hop over to these guys plated through. Details on hole location and size is included in the drill drawing file.

The process of applying copper plating to the pads, traces, and drilled through holes that are to be plated through; boards are put in an electrically charged bath of copper.

This is required when holes are to be drilled through a copper location but the hole is not to be plated through. Prevent this process if possible since it includes expense to the finished board.

The process of using a protective masking product, a solder mask, over the bare copper traces or over the copper that has had a thin layer of solder used; the solder mask secures versus ecological damage, offers insulation, protects against solder shorts, and safeguards traces that run in between pads.

The process of finishing the pad areas with a thin layer of solder to prepare the board for the ultimate wave soldering or reflow soldering process that will occur at a later date after the parts have actually been positioned.

The process of applying the markings for element classifications and part lays out to the board. May be used to simply the top side or to both sides if parts are mounted on both leading and bottom sides.

The process of separating multiple boards from a panel of identical boards; this process also enables cutting notches or slots into the board if needed.

A visual evaluation of the boards; also can be the procedure of inspecting wall quality for plated through holes in multi-layer boards by cross-sectioning or other techniques.

The procedure of looking for continuity or shorted connections on the boards by means using a voltage between numerous points on the board and figuring out if an existing flow happens. Depending upon the board complexity, this process might need a specially designed test fixture and test program to integrate with the electrical test system utilized by the board manufacturer.